Acne is a common skin condition causing pimples on the face and upper torso.
Acne is caused by an interaction between hormones, skin oils, and bacteria, which results in inflammation of hair follicles. Acne is characterized by many types of abnormal growths (lesions): blackheads or whiteheads (comedones), pimples, surface bumps containing pus (pustules), deeper bumps containing pus (nodules), cysts, and sometimes abscesses. Both cysts and abscesses are pus-filled pockets, but abscesses are somewhat larger and deeper.
Sebaceous glands, which secrete an oily substance (sebum), lie in the dermis, the middle layer of skin. These glands are attached to the hair follicles. Sebum, along with dead skin cells, passes up from the sebaceous gland and hair follicle and out to the surface of the skin through the pores.
Acne results when a collection of dried sebum, dead skin cells, and bacteria clogs the hair follicles, blocking the sebum from leaving through the pores. If the blockage is incomplete, a blackhead (open comedone) develops. If the blockage is complete, a whitehead (closed comedone) develops. The blocked sebum-filled hair follicle promotes overgrowth of the bacterium Propionibacterium acnes, which is normally present in the hair follicle. This bacterium breaks down the sebum into substances that irritate the skin. The resulting inflammation causes the skin eruptions that are commonly known as acne pimples. Deeper inflammation causes cysts and sometimes an abscess.
Acne occurs mainly during puberty, when the sebaceous glands are stimulated by increased hormone levels, especially the androgens (such as testosterone), resulting in excessive sebum production. By a person's early to mid 20s, hormone levels usually have decreased enough that acne lessens or disappears. Other conditions that involve hormonal changes can affect the occurrence of acne as well. For example, acne may occur with each menstrual period in young women and may clear up or substantially worsen during pregnancy. The use of certain drugs, particularly corticosteroids and anabolic steroids, can worsen acne or cause acne flare-ups. Certain cosmetics, cleansers, and lotions may worsen acne by clogging the pores. Clothing that is too tight and high humidity and sweating can trigger acne. It is not clear whether milk products and high-glycemic diets (see see Glycemic index) contribute to acne.
Because acne naturally varies in severity for most people—sometimes worsening, sometimes improving—pinpointing the factors that may cause an outbreak is difficult. Acne is often worse in the winter and better in the summer, perhaps because of sunlight's anti-inflammatory effects. There is no relationship, however, between acne and inadequate face washing, masturbation, sexual activity, or most aspects of diet (for example, chocolate or greasy or spicy foods).
Most acne occurs on the face but is also common on the shoulders, back, and upper chest. Anabolic steroid use typically causes acne on the shoulders and upper back.
There are three levels of acne severity: mild, moderate, and severe. Yet even mild acne can be distressing, especially to adolescents, who see each pimple as a major cosmetic challenge.
People with mild acne develop only a few (less than 20) noninflamed blackheads or whiteheads, or a moderate number of small, mildly irritated pimples. Pustules, which resemble pimples with yellow tops, may also develop. Blackheads appear as small flesh-colored bumps with a dark center. Whiteheads have a similar appearance but lack the dark center. Pimples are mildly uncomfortable and have a white center surrounded by a small area of reddened skin.
People with moderate acne have more comedones and pimples and pustules.
People with severe acne have either very large numbers of comedones, pimples, and pustules or cystic (deep) acne. In cystic acne, people have 5 or more cysts, which are large, red, painful, pus-filled nodules that may coalesce under the skin into larger, oozing abscesses.
Mild acne usually does not leave scars. However, squeezing pimples or trying to open them in other ways increases inflammation and the depth of injury to the skin, making scarring more likely. The cysts and abscesses of severe acne often rupture and, after healing, typically leave scars. Scars may be tiny, deep holes (icepick scars); wider pits of varying depth; or large, irregular indentations. Acne scars last a lifetime and, for some people, are cosmetically significant and a source of psychologic stress.
Acne conglobata is the most severe form of acne, causing severe scars and other complications resulting from abscesses.
Doctors base the diagnosis on an examination of the skin. Doctors look for certain symptoms, such as comedones, to determine that the person has acne and not another skin disorder, such as rosacea. After the diagnosis is confirmed, doctors grade the severity of the acne as mild, moderate, or severe based on the number and type of lesions.
Acne of any severity usually lessens spontaneously by the early to mid 20s, but some people, usually women, have acne into their 40s. Some adults develop mild, occasional, single acne lesions. Acne can cause much emotional stress for adolescents and trigger social withdrawal. Counseling may sometimes be needed.
General care of acne is very simple. Affected areas should be gently washed once or twice a day with a mild soap. Antibacterial or abrasive soaps, alcohol pads, and heavy frequent scrubbing provide no added benefit and may further irritate the skin. Cosmetics should be water-based; very greasy products can worsen acne. Although there are no restrictions on specific foods (for example, pizza or chocolate), a healthy, balanced diet should be followed (see see Nutritional Requirements). A low-glycemic index diet and moderation of milk intake might be considered if treatment for acne is ineffective.
Beyond these routine measures, acne treatment depends on the severity of the condition. Mild acne requires the simplest treatment that poses the fewest risks of side effects. More severe acne or acne that does not respond to preliminary treatment requires additional treatment. A treatment plan should always include education, support, and the most practical option for the person. People may need to see a specialist.
Drugs used to treat mild acne are applied to the skin (topical drugs). They work by either killing bacteria (antibiotics) or drying up or unclogging the pores.
The most common topical drug for blackheads and whiteheads is tretinoin. Tretinoin is very effective but is irritating to the skin and makes it more sensitive to sunlight. Doctors therefore use this drug cautiously, starting with infrequent applications and low concentrations, which can both be gradually increased. People who cannot tolerate tretinoin are given adapalene, tazarotene, azelaic acid, and glycolic or salicylic acid.
People who also have inflammation (with pimples or pustules) are given tretinoin combined with benzoyl peroxide, a topical antibiotic, or both. The two most commonly prescribed topical antibiotics are clindamycin and erythromycin. Benzoyl peroxide is available with or without a prescription. Glycolic acid may be used instead of or in addition to tretinoin.
Older nonprescription creams that contain salicylic acid, resorcinol, or sulfur work by drying out the pimples and causing slight peeling.
Blackheads and whiteheads can be removed by a doctor, using instruments called extractors and sterile needles.
Antibiotics taken by mouth (such as tetracycline, minocycline, doxycycline, and erythromycin) can be given to people who have more extensive acne than is manageable with topical drugs alone.
Moderate acne is usually treated with antibiotics given by mouth (orally). Typical antibiotics include tetracycline, doxycycline, minocycline, and erythromycin. Doctors often combine a topical treatment and an oral antibiotic. People may need to take antibiotics for about 12 weeks to achieve the maximum benefits. If possible, oral antibiotics are stopped and topical treatments alone are used to maintain control. Because acne can recur after short-term treatment, therapy may need to be continued for months to years. Women who take antibiotics for a long time sometimes develop vaginal yeast infections that may require treatment.
For the most severe acne, when antibiotics do not work, oral isotretinoin is the best treatment. Isotretinoin, which is related to the topical drug tretinoin, is the only drug that can potentially cure acne. However, isotretinoin can have very serious side effects. Isotretinoin can harm a developing fetus, and women taking it must use strict contraceptive measures so they do not become pregnant. Other, less serious side effects may occur as well. Therapy generally continues for 16 to 20 weeks. If more therapy is needed, it should not be restarted for at least 4 months.
Other acne treatments are useful for specific people. For example, a woman with severe acne that worsens with her menstrual period may be helped by taking oral contraceptives. This treatment takes more than 6 months to produce results.
Doctors sometimes treat large, inflamed nodules or abscesses by injecting corticosteroids into them. Occasionally, a doctor cuts open a nodule or abscess to drain it.
Treatment of severe acne scars depends on their shape, depth, and location. Individual scars of any depth may be cut out and the skin sewn back together. Wide indented scars can be improved cosmetically in a procedure called subcision, in which small cuts are made under the skin to release the scar tissue. This procedure often allows the skin to resume its normal contours. Multiple shallow scars may be treated with chemical peels or laser resurfacing (see see Sidebar 1: Using Lasers to Treat Skin Problems). Dermabrasion, a procedure in which the skin surface is rubbed with an abrasive metal instrument to remove the top layer, also may help remove small scars. Sometimes scars are injected with various substances such as collagen, fat, or a variety of synthetic materials. These substances may raise the scarred area to make it level with the rest of the skin. These injections are temporary and must be repeated every few years.
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Last full review/revision April 2013 by Karen McKoy, MD, MPH